A new service by the co-founder of Twitter aims to encourage small businesses to accept digital transactions by allowing them to swipe credit cards using a smartphone.

It's called Square, and it works with a one-two punch of a free mobile app (iPhone/iPod/iPad, Google Android) and a little plastic cube that plugs into the audio jack of your device.

The service turns anyone with a smartphone into a debit and credit card-accepting small business. So that time you wanted to sell your old gaming rig on Craigslist, but couldn't get someone to pay in cash? Square would fit the bill.

Andrew Nusca is a former writer-editor for ZDNet and contributor to CNET. He is also the former editor of SmartPlanet, ZDNet's sister site about innovation. He writes about business, technology and design now but used to cover finance, fashion and culture. He was an intern at Money, Men's Vogue, Popular Mechanics and the New York Daily Ne...
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